Обсуждение: null values in a view

Hi all,

How could I create a view that returns null values among all other values.
Here is a sample that i want to achieve:

CREATE VIEW view1 AS
SELECT
  attribute1 as a1,
  null as a2
FROM
  table;

Now the problem is that I got an warning:  column "a2" has type "unknown"
I know that I should define a data type for a field a2. But how?
This works with other values but not with nulls:

CREATE VIEW view1 AS
SELECT
  attribute1 as a1,
  text null as a2,
  text 'test' as a3
FROM
  table;



Thanks

-Lauri Kajan

try:

CREATE OR REPLACE VIEW view1 AS
SELECT
  name as a1,
  null::text as a2,
  'test'::text as a3
FROM
  some_table;

Στις Wednesday 05 October 2011 17:22:21 ο/η Lauri Kajan έγραψε:
> Hi all,
>
> How could I create a view that returns null values among all other values.
> Here is a sample that i want to achieve:
>
> CREATE VIEW view1 AS
> SELECT
>   attribute1 as a1,
>   null as a2
> FROM
>   table;
>
> Now the problem is that I got an warning:  column "a2" has type "unknown"
> I know that I should define a data type for a field a2. But how?
> This works with other values but not with nulls:
>
> CREATE VIEW view1 AS
> SELECT
>   attribute1 as a1,
>   text null as a2,
>   text 'test' as a3
> FROM
>   table;
>
>
>
> Thanks
>
> -Lauri Kajan
>



--
Achilleas Mantzios

On Wed, Oct 05, 2011 at 05:22:21PM +0300, Lauri Kajan wrote:
> Hi all,
>
> How could I create a view that returns null values among all other values.
> Here is a sample that i want to achieve:
>
> CREATE VIEW view1 AS
> SELECT
>   attribute1 as a1,
>   null as a2
> FROM
>   table;
>
> Now the problem is that I got an warning:  column "a2" has type "unknown"
> I know that I should define a data type for a field a2. But how?

using normal cast:
null::text as a2

or cast(null as text);

Best regards,

depesz

--
The best thing about modern society is how easy it is to avoid contact with it.
                                                             http://depesz.com/

Lauri Kajan <lauri.kajan@gmail.com> writes:
> This works with other values but not with nulls:

> CREATE VIEW view1 AS
> SELECT
>   attribute1 as a1,
>   text null as a2,
>   text 'test' as a3
> FROM
>   table;

FYI, the syntax  typename 'literal'  works *only* with string literals,
not anything else.  For any other target you have to write
CAST(value AS typename)  or equivalently  value::typename.
CAST is SQL-standard, :: is a Postgres-ism.

            regards, tom lane

This worked.
Thank you all!

I know the casting is quite basic operation but could this be added to
the CREATE VIEW documentation? Now there is only an example:
CREATE VIEW vista AS SELECT text 'Hello World' AS hello;
The same syntax won't work with other type as Tom wrote.


-Lauri

On Wed, Oct 5, 2011 at 5:39 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Lauri Kajan <lauri.kajan@gmail.com> writes:
>> This works with other values but not with nulls:
>
>> CREATE VIEW view1 AS
>> SELECT
>>   attribute1 as a1,
>>   text null as a2,
>>   text 'test' as a3
>> FROM
>>   table;
>
> FYI, the syntax  typename 'literal'  works *only* with string literals,
> not anything else.  For any other target you have to write
> CAST(value AS typename)  or equivalently  value::typename.
> CAST is SQL-standard, :: is a Postgres-ism.
>
>                        regards, tom lane
>